Minimized external electric field on asymmetric monolayer maximizes charge separation for photocatalysis

Controlling charge flow direction is an effective strategy for carrier separation to improve photocatalytic performance. Herein, we create an external electric field (EEF) by chemically loading [Mo 3 S 7 ] 4+ clusters on the S-Zn side of asymmetric ZnIn 2 S 4 (ZIS) monolayers to steer the charge flow. The EEF that stems from the positively charged [Mo 3 S 7 ] 4+ clusters drives photogenerated electrons in the 2D monolayer to the S-Zn side, which are further transferred to the [Mo 3 S 7 ] 4+ clusters through the Mo–S bonds for photocatalytic hydrogen evolution (PHE). This structure exhibits an optimal PHE rate that is four times higher (6.44 mmol g −1  h −1 ) than that of ZIS (1.6 mmol g −1  h −1 ). Furthermore, the significance of the EEF for carrier separation was confirmed via density functional theory calculations based on charge density distribution. This special heterojunction provides a new strategy to accelerate the carrier separation in asymmetric 2D materials.